1. Field of the Invention
The present invention generally relates to motor vehicles, and more specifically to a tire pressure management system for sensing and controlling the air pressure in the tires of a motor vehicle.
2. Description of the Related Art
The pressure to which the tires of a motor vehicle should be optimally inflated depends on the type of terrain over which the vehicle is to be driven. The pressure should be relatively high for hard surfaces such as paved roads, and relatively low for soft surfaces such as wet mud or loose sand.
It is possible to adjust the pressures in the individual tires to a desired value by stopping and exiting the vehicle, manually inflating the tires with a pump to increase the pressure or manually deflating the tires by opening the valves and allowing air to escape to decrease the pressure.
However, this operation is inconvenient and time consuming, and is especially undesirable in inclement weather or in an otherwise hostile environment. It also suffers from the serious disadvantage that it cannot be performed while the vehicle is moving.
U.S. Pat. No. 4,938,272, entitled "VALVE ACTUATOR FOR TIRE PRESSURE MANAGEMENT", issued Jul. 3, 1990 to W. Sandy, Jr. et al, discloses a system including an air pump or compressor mounted on the vehicle body, and conduits leading from the compressor to valves provided in the vehicle wheels. The valves are remotely actuated by the operator from inside the vehicle to connect the compressor to the tires for inflation, or to connect the tires to the atmosphere for deflation.
A disadvantage of Sandy's system is that a high pressure air connection including rotating wheel bearing air seals must be made between the conduits leading from the compressor and the rotating wheels. Such connections are difficult to construct and maintain, and a failure of the connections or valves will result in catastrophic deflation of the tires.
U.S. Pat. No. 4,742,857, entitled "TIRE PRESSURE SENSOR AND AIR SUPPLY TO MAINTAIN DESIRED TIRE PRESSURE", issued May 10, 1988, to S. Ghandhi discloses a system including a high pressure reservoir and a controller valve provided on each wheel. The valves include pressure sensors which are connected to a display on a control unit mounted inside the vehicle. The valves are remotely actuated by the operator from inside the vehicle to connect the reservoirs to the tires for inflation, or to connect the tires to the atmosphere for deflation.
Although Ghandi's system eliminates the high pressure rotary air connections of Sandy's system, the high pressure reservoirs must be periodically replenished from outside the vehicle. This limits the operating range of the vehicle and the number of times it can transition between operating conditions requiring different tire pressures. In addition, the valves are exposed to the atmosphere, and can be contaminated by dirt, sand or other ambient matter.